Commonly-assigned U.S. Pat. No. 4,467,937 to Shaw describes a fuel filler cap assembly in which the cap transmits impact loads to the body of the associated fuel tank by way of mating seal members. Such transfer of impacts is essential in order that the fuel filler cap assembly can pass an applicable drop test for the safety of such tanks. In this drop test, the fuel tank is filled to 90% of its fuel weight capacity with water or the like and dropped, directly on the fuel cap, from a height of 10 feet, onto a steel plate. According to the Shaw patent, the fuel cap should be constructed such that impacts from such planar surfaces are transmitted through the cap directly into the structure of the tank.
The cap shown in the Shaw patent has met with substantial commercial success. Applicant desired to improve its structure further by reducing the amount of material required to form its principal component, the cap body member. Moreover, the Shaw device as commercially produced includes a poppet valve for releasing overpressure of gas within the associated fuel tank. The flow capabilities of poppet valves are limited by the flow area around the valve head when the valve is open. It was designed to increase this gas flow region.
The cap shown in the Shaw patent also requires careful adjustment of the axial position of the retaining member 10 with respect to the cap body member, as this relation controls the integrity of the seal between the cap body member and the filler adapter provided on the fuel tank. It was desired to simplify the assembly procedure required, thus reducing cost.
In conjunction with these improvements, it was also desired to retain certain desirable features of the Shaw cap, namely a weather protected key lock securing the fuel tank assembly, attractive appearance, and proper tactile characteristics for the user of the cap. It was also desired to ensure that rain, snow, mud or other debris would not accumulate on the cap.